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. 2019 Jul 10;10:881. doi: 10.3389/fpls.2019.00881

FIGURE 1.

FIGURE 1

Diversification of primary metabolic pathways and enzymes in plants. Although primary metabolism is highly constrained and generally assumed to be conserved within the plant kingdom, there are examples of evolutionary diversification of some primary metabolic pathways (blue). Many of them likely supported diversification of downstream specialized metabolism (green letters) as enabling or associated traits. Blue letters and boxes denote alternative routes or enzymes to synthesize key primary metabolite precursors. Green arrows and letters indicate specialized metabolic pathways derived from these primary precursors. Dotted red lines indicate feedback inhibition that act specifically on canonical leucine (Leu), tryptophan (Trp), and tyrosine (Tyr) biosynthetic pathways, but not on “lineage-specific” alternative enzymes. ADT, arogenate dehydratase; ASα, anthranilate synthase α subunit; BS, bundle sheath cells; E4P, erythrose 4-phosphate; 4HPP, 4-hydroxyphenylpyruvate; iC4-CoA, 2-methylpropanoic-coenzyme A; iC5-CoA, 2-methylbutanoic-coenzyme A; IPMS, isopropylmalate synthase; IPP, isopentenyl diphosphate; MEP, methylerythritol phosphate; 3MOB, 3-methyl-2-oxobutanoate; MS, mesophyll cells; MVA, mevalonate; PDT, prephenate dehydratase; PEP, phosphoenolpyruvate; 3PGA, 3-phosphoglycerate; PPA-AT, prephenate aminotransferase; PPY, phenylpyruvate; TAG, triacylglycerol; TyrAa, arogenate dehydrogenase; TyrAp, prephenate dehydrogenase; Val, valine; VLCFA, very long chain fatty acid.